Designing a waveguide to transmit sound to a dolphin in a functional magnetic response imaging machine

Abstract

Functional Magnetic Resonance Imaging (fMRI) offers great opportunities to learn how a dolphin’s brain processes acoustic echolocation and communication signals. Delivering sound to an animal in a fMRI requires a sound delivery system with no ferrous metal. This talk proposes an approach that generates sound far from the fMRI magnet and then conducts the sound through a waveguide to the dolphin roughly 10 m away. The waveguide functions at two frequency ranges are 80 kHz for echolocation signals and 10 kHz to 20 kHz for communication signals. This approach has two challenges: will there be enough energy for the dolphin to hear the acoustic signals and will the received signal be distorted? The waveguide loses energy due to the radiation impedance around the hydrophone, absorption and friction, and the impedance mismatch between the waveguide and the dolphin. Filling the waveguide with water limits the transmission loss through the waveguide. The waveguide radius will be chosen to limit the number of trapped modes, minimizing distortion due to dispersion.